You referred me to the Open Source version documents. Unless they are basically the same.

OK. Maybe it isn't clear to me.

But, even though I have built the 4.5.6 server, your suggestion I just delete it - to rebuild the box again? Then just copy across the /opt/zimbra directory. As far as I can see there is mySQL databases as well - unless Zimbra doesn't use them? Then just copying files could be very messy.

Surely there is an easier (less dangerous) migration path/tool to do this.

Some considerations should be
1) DNS-make sure that mx records get transferred to the new box.
2) Move over (once you've backed up) the entire /opt/zimbra/backups, if that's where you backed up. If not, move your other location
3) make sure the files are Zimbra user accessable.